C04_01

Analysis of solar minima by using radiocarbon in tree-rings

Brehm N¹, Christl M¹, Synal H¹, Bayliss A², Nicolussi K³, Pearson C⁴, Bleicher N⁵, Brown D⁶, Wacker L¹

¹Eth Zürich, Zürich, Switzerland, ²Historic England, London, UK, ³Universität Innsbruck, Innsbruck, Austria, ⁴University of Arizona, Tucson, USA, ⁵Underwater archaeology and Dendroarchaeology, Zürich, Switzerland, ⁶ The Queen’s University, Belfast, UK

The Sun provides virtually all the principal energy input to the Earth’s climate system and solar variability is a significant external climate forcing. While direct observations of the sun’s activity via sunspots only cover the last about 400 years, cosmogenic radionuclides such as ¹⁴C, 10Be and 36Cl stored in tree-rings and ice cores serve as  solar activity proxies extending back thousands of years.

¹⁴C is produced continuously in the Earth’s atmosphere by highly energetic cosmic rays. The rate of production depends on solar activity and geomagnetic field strength. Dendrochronologically dated trees represent the most reliable archive for reconstruction of the past atmospheric ¹⁴C concentration over the past 14 000 yr, because of the absolute dating of a tree ring and the tree’s capability to record the atmospheric ¹⁴C concentrations at annual resolution.

Here we present two annually resolved records of atmospheric ¹⁴C covering two different solar minima and the following solar maxima. The new data, which covers the time periods from 5450-5000 and 1950-2400 years BP, is analyzed by using a carbon cycle box model to reconstruct past solar activity. The reconstructed high-resolution solar activity records are compared with the solar activity recontructed from the Spörer and Maunder minima which occurred during the last millennium. The data gives more high resolution insight on two of the most extreme solar minima during the past 6000 years.